The invention concerns a gas dynamic pressure wave supercharger for internal combustion engines.
In pressure wave superchargers for supercharging vehicle internal combustion engines, the problem of the axial clearances between the rotor end surfaces and the casing end surfaces facing the rotor is of great importance. The efficiency and the operating behaviour of a pressure wave supercharger depend very strongly on these axial clearances. Satisfactory operation of the pressure wave supercharger and good efficiency can only be obtained using very small axial operating clearances because the leakage losses at the end faces of the rotor are then minimized. However, the rotor must be simultaneously prevented from touching the casing end surfaces. Because thermal expansion does not displace the end surfaces simply in parallel planes, this danger cannot be dealt with by larger fitting clearances alone. To this problem must be added the danger of rubbing occurring between the rotor and the casing end surfaces facing it because of rotor vibrations.
In order to avoid rotor damage due to possible heavy contact, an abradable layer, for example a graphite/nickel layer, can be applied to the casing or rotor end surfaces, or an abrasive fine grain AL.sub.2 O.sub.3 (corundum base) layer can be applied to the casing end surfaces.
The rubbing layer is only abraded in the radial region of the relatively sharp-edged cell walls. The layer in the region of the thick hub tube is merely compressed, which can lead to the rotor becoming jammed in the case of severe rubbing. Due to ageing of the layer, the latter can flake off and hence lead to poor efficiency of the pressure wave supercharger. In addition, the rubbing layer applied by a flame-spray method is too expensive for mass production of a pressure wave supercharger.
The object of the invention is to produce a gas dynamic pressure wave supercharger, of the first type mentioned. The rotary and casing end surfaces of the supercharger avoids rubbing layers and is optionally shaped with respect to thermal expansion and rotor vibrations, guaranteeing satisfactory operation of the pressure wave supercharger.
The supercharger comprises a rotor located between an air casing and a gas casing. The rotor end surfaces are each separated by an axial clearance from the casing end surface facing the rotor. On the air casing side, at least one of the two mutually facing end surfaces of the rotor and the air casing is convex. The shape serves to maintain an axial clearance when the motor operates from a cold startup. Alternatively, on the gas casing side of the rotor at least one of the two mutually facing end surfaces may be concave.
The advantages obtained by means of the invention may be seen essentially in that the thermal expansion and rotor vibrations are so compensated by appropriate shaping of the rotor and casing end surfaces that it is possible to operate with very small axial clearances and hence with a good efficiency.